A number of liquids exhibit properties which are normally associated with crystalline solids and such materials have often been referred to as "ordered liquids". Such ordered liquids effectively exist in states or phases which are intermediate between an isotropic liquid phase, where molecules thereof are randomly oriented and not arranged on a three-dimensional lattice, and a crystalline solid phase wherein the molecules are positioned at well-defined sites on a three-dimensional lattice and are oriented with respect to the lattice. Materials in such intermediate phases are sometimes designated as "mesophases". One group of such mesophases has been designated as "liquid crystals" which materials are finding greater use, particularly as materials for display purposes such as in wrist watches, calculators, panel meters, and the like.
One of such mesophases, or mesomorphic states, is the nematic state which can be formed on cooling from an isotropic liquid melt. In the nematic state the molecules are not fixed on any kind of lattice and they are free to move about, imparting to the material the property of fluidity, but the molecules, which are generally elongated, tend to align with respect to each other, PG,5 imparting a long-range orientational order to the liquid.
A second mesomorphic state is the smectic state which displays a greater degree of order than the nematic state. The molecules tend to exhibit a long-range orientational order and further order themselves by forming substantially planar layers. Other mesophases include the cholesteric phase and the lyotropic liquid crystals.
The major application for nematic liquid crystals has been in display devices. Several different types of nematic liquid crystal displays have been described but all have the property that the surfaces which contact the liquid crystal layer are treated in such a manner as to produce a predetermined orientational alignment of the liquid crystal molecules. In one particular type of display, such nematic liquid crystals are placed within a display device between two surfaces which have been treated so that the molecules of the liquid crystal adjacent the oppositely disposed surfaces are aligned orthogonally, the molecules therebetween being aligned at angles therebetween so that the overall device is said to comprise a "twisted nematic" liquid crystal display, as is well known in the art.
In order to comprise a useful device, said "twisted nematic" display must include a polarizer of light on each side of the twisted nematic liquid crystal layer with the polarizing directions of said polarizers selectively oriented with respect to each other and to the liquid crystal layer. Also, electrically conducting plates must be placed on opposite sides of the liquid crystal layer in order to modify the alignment of the intermediate liquid crystal by the application of electrical fields, but said conducting plates must be relatively transparent to light in order to permit passage of light through the device consisting of polarizers, conducting plates, and the twisted nematic layer.
Alignment of the molecules of ordered liquids such as liquid crystals has been achieved in the past by placing the liquid crystal in contact with a surface which has been made relatively anisotropic so that the molecules align along a specified direction. The treatment of the surface has been obtained in various ways. For example, the surface is often rubbed with an abrasive as described in the article by Creagh and Kmetz, Mol. Cryst. and Liq. Cryst. 24, 59 (1973). Other techniques have utilized directed oblique evaporation of silicon monoxide as described in the articles by Janning, Appl. Phys. Lett. 21, 173 (1972) and Dixon et al., Appl. Phys. Lett. 24, 47 (1974), the latter also suggesting the use of parallel grooves but nowhere disclosing any specific process that could be successfully used for such purpose. Still others have suggested the technique of dipping the surface in surfactants as described in the article of Proust et al., Solid State Communications 11, 1227 (1972). Others have scratched the surface with a diamond pencil, as discussed by Wolff et al., Mol. Cryst. and Liq. Cryst., 23, 187 (1973).
Such techniques have been used for aligning nematic liquid crystals and it is believed that such alignment minimizes the free energy associated with elastic deformation of the liquid crystal. Oblique evaporation and rubbing techniques tend to produce surfaces with a topography that is largely uncontrolled and, in the case of rubbing techniques, particularly difficult to reproduce. Oblique evaporation further does not permit arbitrary alignment since such techniques can generally only be readily used for aligning molecules in a single specified direction. Moreover, while the quality of alignment may be useful in many applications, other applications requiring higher quality alignment will not be able to effectively use surfaces which have been treated by oblique evaporation techniques. While the use of surfactants has produced alignment, often such alignment is of a semi-permanent nature only and will, in effect, disappear over a reasonable time period. Moreover, in some applications the surface which has been treated with surfactants must be subsequently processed at a relatively high temperature which can effectively destroy the surfactant as well as the alignment which has been achieved thereby. Anisotropy produced by rubbing may also be destroyed by high temperature sealing of liquid crystal cells.
Accordingly, it is desirable to provide a process for treating a surface which improves the quality of alignment or orientation thereof so that mesophases can be permanently and reliably aligned in a substantially reproducible fashion. Furthermore, a process is desired which is well-suited for producing patterns of liquid crystal alignment more complex than the generally unidirectional alignment which is easily obtained with the prior art methods. With respect to liquid crystal display devices utilizing twisted nematic liquid crystals, such devices normally utilize separate polarizing elements, separate elements for aligning the liquid crystals, and additional separate elements for providing the desired electric field therein. It is desirable to obtain such a structure in a way which would reduce the present costs thereof and also provide for a relatively more rugged structure than is currently available for such purpose. Less expensive display devices which are less easily damaged by high temperature or humidity should find an even broader market than presently available liquid crystal display devices.